With regard to an engine (internal combustion engine) of a car such as a vehicle, it has been examined that, for the purpose of the improvement of a warm-up performance of the engine, the improvement of a fuel efficiency by moving the engine at an appropriate temperature and the like, by providing, besides a main passage which circulates coolant between the engine and a radiator, a bypass passage which bypasses the radiator and returns the coolant directly to the engine, and by providing a coolant control valve in the main passage, and further by controlling an opening degree of this coolant control valve according to a coolant temperature and other values, an amount of the coolant that is flown in the main passage and is cooled off by the radiator is controlled. Incidentally, the coolant water is circulated by a pump that is driven by the engine or an electric motor, more specifically, the coolant water is circulated mainly in the main passage while the engine is operated and the coolant control valve is opened, and the coolant water is circulated in the bypass passage while the coolant control valve is closed.
For example, at the engine starting or the like, when the coolant temperature is low, by blocking the main passage and returning the coolant from the bypass passage directly to the engine without allowing the coolant to pass through the radiator, warm-up of the engine is promoted. Also, for example, for controlling the temperature of the coolant so as to optimize combustion of fuel in the engine after the warm-up, opening and closing (the opening degree) of the coolant control valve is controlled. As such a coolant control valve, use of, for example, a rotary valve that is driven by a stepping motor or the like are examined (for example, see Patent Literature 1).
The rotary valve requires motive power both when being changed from an opened state to a closed state and when being changed from the closed state to the opened state, but can have a structure that does not require such motive power both while maintaining its opened state and while maintaining its closed state, which exhibits an effect of saving energy comparing to a valve that requires energy for maintaining its closed state or opened state.